Some modern mobile devices (e.g., media player, smartphone) include a pedometer function that uses built-in sensors to estimate a user's step frequency during walking or running. The pedometer records the user's total daily steps as well as individual workouts. The device can be placed in the user's pocket or attached to the user's clothes (e.g., attached to a waistband). The user can synchronize data stored on the device to a website that can track the user's daily physical activity and fitness goals, or the data can be uploaded to a social network where it can be shared with friends.
Because each user has a different step frequency for walking or running, distance measurements can sometimes be inaccurate. One approach to improving accuracy is to scale the distance estimate with a calibration factor to correct for error in step frequency due to the user's unique stride. A different calibration factor may be calculated for walking and running after the user completes a workout while wearing the mobile device.